Magnetic disks and disk drives are conventionally employed for storing data in magnetizable form. Preferably, one or more disks are rotated on a central axis in combination with data transducing heads positioned in close proximity to the recording surfaces of the disks and moved generally radially with respect thereto. Data are written onto and read from a rapidly rotating recording disk by means of a magnetic head transducer assembly that flies closely over the surface of the disk. Preferably, each face of each disk will have its own independent head.
In a magnetic media, digital information (expressed as combinations of “0's” and “1's”) is written on tiny magnetic bits (which themselves are made up of many even smaller grains). When a bit is being written, a magnetic field produced by the disc drive's head orients the bit's magnetization in a particular direction, corresponding to either a 0 or 1. The magnetism in the head in essence “flips” the magnetization in the bit between two stable orientations.
Magnetic thin-film media, wherein a fine grained polycrystalline magnetic alloy layer serves as the active recording medium layer, are generally classified as “longitudinal” or “perpendicular,” depending on the orientation of the magnetization of the magnetic domains of the grains of the magnetic material. In longitudinal media (also often referred as “conventional” media), the magnetization in the bits is flipped between lying parallel and anti-parallel to the direction in which the head is moving relative to the disc. In perpendicular media, the magnetization of the disc, instead of lying in the disc's plane as it does in longitudinal recording, stands on end perpendicular to the plane of the disc. The bits are then represented as regions of upward or downward directed magnetization (corresponding to the 1's and 0's of the digital data).
FIG. 1 shows a disk recording medium and a cross section of a disc showing the difference between longitudinal and perpendicular recording. Even though FIG. 1 shows one side of the disk, magnetic recording layers are usually sputter deposited on both sides of the non-magnetic aluminum substrate of FIG. 1. Also, even though FIG. 1 shows an aluminum substrate, other embodiments include a substrate made of glass, glass-ceramic, aluminum/NiP, metal alloys, plastic/polymer material, ceramic, glass-polymer, composite materials or other non-magnetic materials.
Efforts are continually being made to increase the areal recording density, i.e., the bit density, or bits/unit area, and signal-to-medium noise ratio (SMNR) of the magnetic media. To continue pushing areal densities and increase overall storage capacity, the data bits must be made smaller and put closer together. However, there are limits to how small the bits may be made. If the bit becomes too small, the magnetic energy holding the bit in place may become so small that thermal energy may cause it to demagnetize over time. This phenomenon is known as superparamagnetism.
Perpendicular recording media are being developed for its capability of extending the areal density to a much higher level without the similar thermal stability limit that longitudinal media are facing. One of the major designs for perpendicular recording media utilizes reactive sputtering the magnetic layer in a gas mixture of oxygen and the popular inert gas Ar, to produce so called granular perpendicular media. The magnetic layer produced by this way has oxide mainly in grain boundaries, which effectively breaks down exchange coupling and results in better recording performance.
The tendency for neighboring magnetic dipoles in a material to line up parallel or antiparallel to each other is called exchange (or exchange coupling). Basically, exchange results from the overlap of orbiting electron on adjacent atoms. The atomic moment of an atom is proportional to the angular momentum of the atom. This angular momentum consists of orbital angular momentum due to the rotation of electrons in their orbits and spin angular momentum (called “spin” for short) which is due to the rotation of electrons about their own axes. If the spin angular momentum of two electrons on neighboring atoms is s1 and s2, then the energy of this pair of electrons, E, is given by E=−2J s1*s2, where J is a constant called the exchange integral. In ferromagnetic materials, J is positive and the moments of adjacent atoms point in the same direction. In antiferromagnetic materials, J is negative. In an antiferromagnetic material, the moments of adjacent atoms point in opposite directions.
Exchange is largely a nearest-neighbor phenomenon that occurs across distances typical of the distance between atoms in a solid (a few angstroms). If there is one atomic boundary layer of one material such as an oxide in grain boundaries, then that may be enough (though thicker boundary layer could also be used) to break down the exchange coupling between the grains separated by the boundary layer. Thus, granular media (i.e., media that grain and have amorphous material such as an oxide and/or voids between crystalline grains) with laminated film structures consisting of laminated soft magnetic layers, seed layers, such as Ag, Au, Cu etc., Ru-alloy inter layers, CoPt-based magnetic recording layers containing oxides, and carbon overcoats have been made and found promising for perpendicular magnetic recording application. However, it has been found that the media coercivity, Hc, and signal-to-media-noise ratio, SMNR, of the prior art perpendicular recording media need to be enhanced significantly for high-density recording applications. This invention relates to perpendicular recording media with enhanced properties for high-density recording.